where the sum extends over the neigbours of spin \(i\) . Note that the
reversal of a spin at a given field \(H\)  may induce the reversal of
some of its neigbours at the same field \(H\) . Such collective events
are the so called avalanches that end when all the spins are stable.
Only after the avalanches have finished, the external field is varied
again. It has been shown that, during a monotonous driving of the
external field, no reverse spin-flips may occur and, moreover, the
model exhibits the so called abelian property: i.e. the final states
do not depend on the order in which the unstable spins are flipped.
In the thermodynamic limit, the system with this metastable dynamics
also shows a critical point at \(\sigma _c^{met}=2.21\) 
[1]}, [2]}, below which the metastable trajectory exhibits
a discontinuity.
